1. Field of the Invention
The present invention relates to a photographic roll film, especially 120-size or 220-size roll film.
2. Description of the Related Art
ISO120-size and 220-size roll films are well known as Brownie film in the art which both have an appearance as shown in FIG. 29. In a 120-size roll film 1, a filmstrip 2 is secured to a light-shielding backing paper 3 which extends over the filmstrip 2, as is shown in FIG. 30. A 220-size roll film uses a longer filmstrip than 120-size, while a backing paper is replaced by a leader paper and a trailer paper which are secured to opposite ends of the elongated filmstrip. Thus, the 220-size roll film has a larger number of available exposure frames, compared with the 120-size. In both sizes, the filmstrip is coiled around a spool 5.
The spool 5 is standardized according to ISO 732-1982, ANSI PHI 21-1980, JIS K7512-1985 etc., which is constituted of a spool core 6, a pair of flanges 7 provided on opposite ends of the spool core 6, and a slit 8 formed along the spool core 6, as is shown in FIG. 31. The flanges 7 confine and align edges of the backing paper 3 rolled on the spool core 6.
To manufacture the roll film 1, a trailer 3b is inserted in the slit 8. Then, the spool 5 is rotated to coil the filmstrip 2 with the backing paper 3 around the spool core 6. Thereafter, a leading end 3a of the backing paper 3 is bent and is secured with an adhesive tape 9 to prevent unwinding. In a center of each end face of the flanges 7, there is a chucking groove 10 to be engaged with a key shaft of a camera.
To load the roll film 1, another spool having the same construction as the spool 5 should previously be positioned in a film take-up chamber of the camera. After opening a rear lid of the camera, the photographer first peals off the tape 9 while holding the backing paper 3 so as not to unwind. Then, the chucking grooves 10 are engaged with the key shafts of a film supply chamber of the camera.
The leader 3a is then inserted in the slit 8 of the spool 5 in the film take-up chamber, hereinafter referred to as a take-up spool, as is shown in FIGS. 31 and 32. Then, a windup lever of the camera is operated to rotate the take-up spool 5 to wind the backing paper 3 around the spool core 6 of the take-up spool 5 more than one turn, usually two or three turns. When the leader 3a is thus secured to the take-up spool 5, the rear lid is closed, and the windup lever is further operated to position the filmstrip 2 in an appropriate exposure position.
After each exposure, the windup lever is operated to wind up the exposed frame of the filmstrip 2 onto the take-up spool 5. When all available frames have been exposed, the windup lever is allowed to be operated without stop, so that the entire length of the roll film 1 is wound up onto the take-up spool 5. Thereafter, the rear lid is opened to remove the exposed roll film 1. Then, the trailer 3b, which is now on the outermost convolution of the roll, is secured with an adhesive tape. The spool 5 left in the film supply chamber is replaced in the film take-up chamber for the next loading of an unexposed roll film.
However, because the leader 3a is apt to slip off the slit 8, the photographer should hold the backing paper. 3 so as not to slip off the slit 8 while operating the windup lever. This is obviously inconvenient. Moreover, if the leader 3a is not properly wound on the spool 5, e.g. if the leader 3a is deviated in the axial direction relative to the spool 5, the deviation would increase with increasing number of turns, and the edge of the backing paper 3 is bent to loosen the roll on the spool 5. As a result, light-tightness between the edges of the backing paper 3 and the flanges 7 is lowered so that the filmstrip 2 can be fogged.
Several solutions have been suggested to prevent the slip. For example, JPA 1-251030 provides protrusions in the slit to increase frictional resistance between the light-shielding paper or backing paper and the spool; JPA 2-235052 provides cutouts through the leader of the light-shielding paper, so as to be engaged with projections in the slit of the spool; JPA 2-137842 makes surface deformation treatment on either or both of contacting surfaces between the spool and the leader of the light-shielding paper, so as to be engage with each other; and JPA 2-160231 shapes the spool to have a particular edge angle between the spool core periphery and the inner surface of the slit.
However, any of the above known solutions do not completely prevent the slip-off of the leader so that it is still necessary to hold the leader to the slit of the spool with the fingers until the leader has been securely wound around the spool. Thus, none of these known spools achieve sufficiently easy and reliable loading and preliminary winding of the 120 or 220-size roll film.
On the other hand, there are various spools for 35 mm or ISO 135-size roll film that has claws in a slit to engage with holes of a film leader. U.S. Pat. No. 1,930,144 even suggests that the spool disclosed therein is applicable to those roll films which are attached with light-shielding paper. However, all of the spools suggested for 135-size roll film designate the direction to insert the film leader into the slit. Therefore, if such a spool could be used for 120 or 220-size roll film, it would be necessary to insert the leader of the light-shielding paper from the right direction into the slit of the spool placed in the film take-up chamber at every film loading. That would lower the efficiency of loading, and could cause improper preliminary winding. It has been difficult to automatize the loading and preliminary winding of the 120 or 220-size roll film.